Thermally controlled assembly

ABSTRACT

A thermally controlled assembly having two parallel PCBs defining there between, and by the aid of a channel forming element, a channel in which air is forced, using a fan, to cool components in the channel. The fan has a cooling surface cooled by air from the fan and which is biased toward an element provided in a space below the cooling surface. The forced air also drawing air from outside the assembly through the space and into the channel to cool other elements provided in the space.

The present invention relates to a method of cooling electroniccomponents using a channel in which cooling air is passed. Technologieslike this are known from e.g. HiFi amplifiers in which cooling elementswith cooling fins are positioned with the fins directed inwardly intothe channel in which a fan drives cooling air. The electronic componentsare positioned on the outer sides of the cooling elements.

Presently, the cooling is performed on components positioned at or fixedto PCBs and especially the forming, using the PCBs, of a channel throughwhich air is forced in order to cool the components

In a first aspect, the invention relates to an assembly comprising:

-   -   a first PCB with a first side and a second side, one or more        first electrical components being positioned at the first side        of the first PCB,    -   a second PCB with a first side and a second side, one or more        second electrical components being positioned at the first side        of the second PCB, the first side of the first PCB facing the        first side of the second PCB,    -   a channel forming element forming, with at least part of the        first sides of the first and second PCBs a channel having a        first end and a second end, a slit being provided in the channel        forming element, and    -   an air forcing element positioned to force air through the        channel from the first end thereof toward the second end        thereof, the air forcing element comprising a cooling surface        and biasing elements biasing the cooling surface against at        least one component of the first or second components, the        cooling surface defining a space wherein the at least one        component is positioned,    -   the slit being positioned so that air may be drawn there        through, due to the venturi effect, and into the space and into        the channel.

The present invention provides a number of advantages in that space maybe saved without loosing cooling of the components. Thus, when the firstsides of the PCBs are used to shape or form the channel, direct coolingof the components positioned in the channel is obtained and noadditional elements are required to form the cooling channel. Inaddition, the channel forming element may also be provided rather stiffand thus also act to stiffen the assembly. This is especially relevantwhen, as is described further below, this element is also used forengaging biasing means.

In the present context, an assembly is a number of elements operatingtogether and/or being connected to each other, such as fixed to eachother. Naturally, the fixing may be obtained in a detachable manner, andany inter-operation may be carried out via wires, wirelessly, viamechanical coupling, or the like.

An electronic component may be any type of component from a simpleresistor to a chip of any kind. Thus, components may be processors,FPGAs, memory circuits, resistors, capacitors, coils/inductors or thelike.

Usually, a PCB is a printed circuit board, which is a flat element withtwo primary sides and a rim portion. A PCB may have one or more layersof conductors and may have electrical components on one side thereof oron the two primary sides thereof. Usually, the electrical componentswill be able to inter-operate by sending/receiving power and/or signalsbetween each other via conductors in the PCB. Normally, the componentsare fixed to the PCB, such as via conductors thereof.

When the first sides of the PCBs face each other, these sides form sidesof the channel in which electrical components positioned at the firstsides are positioned so as to be cooled by the air flow generated by theair forcing element.

Preferably, the first and second PCBs are parallel, which means that thegeneral planes thereof, which will be the major planes of the PCBs inthe situation where these are flat elements, are parallel. In thissituation, the edge portions of the PCBs may be positioned with the samedistance there between so that the channel forming element may have thesame thickness at the positions at which the channel is formed.

In this context, the channel forming element is adapted to form thechannel together with the PCBs, such as the first sides of the PCBs andthe electrical components positioned at the first sides at the parts ofthe PCBs forming the channel.

Naturally, the channel may be straight, curved or meandering, both in aplane of one or both of the first sides or perpendicular thereto. It isnoted that the components positioned at the first sides may cause thechannel to be irregular in internal dimensions so that the air flowtherein is affected.

It is noted that also in the situation where the PCBs are parallel (mainplanes when the PCBs are flat elements), the channel forming elementneeds not be positioned at straight sides of the PCBs but may define thechannel over only a part of the first surfaces also across a width ofthe channel perpendicular to the overall direction of the channel fromthe first end to the second end.

The forming of the channel will be the providing of elements causing theair to flow generally from the first end to the second end. Naturally,the channel forming element needs not seal the channel in an air tightmanner along the full length of the channel. Small openings throughwhich air may enter or exit the channel are acceptable and may actuallyaid in the venting and cooling, as long as the desired air flow ismaintainable in the channel.

The channel preferably has a first end and a second end at which air mayenter or exit the channel. The entering/exiting of air into/from thechannel may be via one or more openings. Other openings may bepositioned not at the ends in order to obtain a desired air flow in thechannel.

The simplest manner of forming the channel is to have the channelforming element simply provide a sealing between edges of the PCBs thusforming the channel using the full width of the PCBs across the generaldirection of the channel (such as from the first to the second end).However, the channel may be made more narrow than that by having thechannel forming element engage or seal not at the edge(s) of one or bothPCBs but seal or engage at the first surface thereof. Thus, one PCB maybe wider, in the direction across the general direction of the channel,than the other, so that the channel could take up the full width of oneof the PCBs but not the other, or the channel forming element engages orseals at the first surface of both PCBs and may then be more narrow thanthe width, across the general direction of the channel, of both PCBs.

Usually, the channel will have a general direction along a longitudinalaxis of one or both PCBs, so that the ends will be at or near the edgesof this/these PCB(s) at the ends thereof.

A number of means and manners exist for forcing air into e.g. a channel.Fans, compressed air or the like may be used. Providing suction at oneend of the channel will force the air in one direction through thechannel and providing an increased pressure (operating e.g. a fan in theopposite direction) will force the air in the other direction throughthe channel. The desired direction of the air will depend on thepositions of the components in the channel and in particular theposition of the most heat generating and most heat sensitive of thecomponents within the channel.

It may be desired that the coolest air, i.e. air that has not been usedfor cooling a number of the components, is provided firstly to the mostheat sensitive elements in order to first and foremost ensure cooling ofthese elements. Alternatively, it may be desired to position the mostheat generating components close to the point of exit of the air fromthe channel in order for the heated air generated thereby to not beprovided to other components, which could heat these instead of coolingthese components.

Thus, the direction of flow of the air in the channel as well as thepositions of individual components may be used for tailoring the coolingof individual components.

As mentioned, the air may be forced into the channel at one end andoutput at the other. Usually, the channel has one or more openings atthe ends thereof in order to facilitate this air flow. Other openingsmay also be provided if desired.

The air forcing element comprises a cooling surface and biasing elementsbiasing the cooling surface against at least one component of the firstor second components. Thus, whereas the components in the channel formedby e.g. overlapping parts of the first and second PCBs are cooled by theair flowing through the channel, some components are alternatively oradditionally cooled directly by the cooling surface biased there on. Itis noted that the cooling surface would usually be biased only on thehighest of the components, whereas cooling of lower components (in thedirection perpendicular to the plane of the PCB) is then obtained by airflow or by providing a thermally conducting element or material betweensuch components and the cooling surface. Also, or in addition, suchlower components can be cooled by providing a thermally conductingelement or material between such components and the cooling surface.

In one embodiment, the assembly further comprises one or more openingspositioned at or near the second end of the channel. As mentioned above,one or more of such openings may be positioned in the channel formingelement.

In that or another embodiment:

-   -   the first PCB has a first outline, in a plane thereof,    -   the second PCB has a second outline, in the plane, at least a        part of the first and second outlines being overlapping, the        channel forming element blocking or closing any opening between        the first and second PCBs at at least part of a boundary of the        overlapping part of the outlines.

Thus, the outlines of the first and second PCBs overlap, and the channelforming element may use the overlapping parts of the PCBs to form thechannel.

In a particularly interesting embodiment, the first PCB covers a firstarea, in a plane thereof, the second PCB covers a second area in theplane, the second area being positioned within the first area, and theair forcing element covers a third area, in the plane, the third areabeing positioned within a part of the first area not covered by thesecond area. Thus, the air forcing element may be positioned adjacent tothe second PCB and over a part of the first surface of the first PCB.Again, the channel will be formed where the first and second areasoverlap, and an opening for air exit/entering may be positioned at aninterface between the second and third areas. As will be describedfurther below, this brings about advantages.

Preferably the second and third areas do not overlap but together coveror correspond to the first area in order to utilize the space of theassembly as optimally as possible.

In this embodiment, in the plane, the air forcing element is preferablypositioned closer to the first end of the channel than the second end ofthe channel. Thus, the air forcing element is used for forcing air fromoutside the assembly through the air forcing element and into thechannel. The air will then flow through the channel and the componentspositioned therein and out at the other end of the channel.

An embodiment which is easy to set up is one wherein the first andsecond PCBs are at least substantially parallel. In this situation, thechannel forming element may have the same thickness or extent in thedirection perpendicular to the plane of the PCBs in order to obtain itsfunction.

In order to increase the cooling of the cooling surface, the air forcingelement preferably comprises a number of fins through which the airentering the channel passes and which are thermally connected to thecooling surface.

In general, it is preferred that the biasing elements comprise at leastthree resilient elements having at least substantially the same springconstant, the resilient elements being positioned so that the forceexerted by the biasing elements and the air forcing element on the atleast one component is perpendicular to a plane of the PCB at which theat least one component is positioned.

In this respect, a resilient element may be any type of resilientelement, such as a spring, helical or blade spring, a foam, a solidmaterial, such as rubber, plastics, polymer or the like. Naturally, alsomore complicated technologies, such as compressible gas cylinders or thelike may be used if desired. The spring or resilient constant of theresilient element will usually describe the force required to perform apredetermined deformation/compression of the element in a particulardirection.

When the force is perpendicular to the plane, the cooling surface willbe able to contact at least substantially all of an upper surface of thecomponent, which normally is a flat component having an upper surfaceparallel with the plane of the PCB. This optimizes the cooling of thiscomponent.

In addition, providing the force perpendicular to the plane of the PCBensures that the biasing does not stress any attachment of the componentto the PCB.

In a very interesting embodiment, the biasing elements are positioned sothat, along each of two axes perpendicular to each other and positionedin the plane, a first combined distance from a centre of the at leastone component to each biasing element positioned in one direction alongthe axis in relation to the centre is within a predetermined distancefrom a second combined distance from the centre to each biasing elementpositioned in the opposite direction along the axis in relation to thecentre. Ideally and preferably, the predetermined distance is zero, butmanufacturing imperfections and other considerations may dictate that acertain deviation there from is tolerated. Thus, this distance may be upto 10% of a largest distance from any resilient means to the centre ofthe component.

Thus, for each of the two axes the directions are determined from thecentre of the component; the distances along the two directions aresimply added up.

It may be irrelevant how the axes are chosen. The relevant part is thatthe force exerted on the component relates to the distance from thecentre to the resilient element and the force exerted, which preferablyis the same for all resilient elements.

This embodiment is particularly relevant when the biasing elementscannot be positioned symmetrically around the component with the samedistances to the centre of the component. This may be the case whereelectronic components, the air forcing element or the like prevent thisor make it difficult. The choice that the biasing elements should havethe same resiliency or spring constant then makes selection of suchpositions difficult.

The above determination of the positions, however, ensures that theforce remains perpendicular to the plane of the PCB even when the springconstants are identical. Thus, the same, advantageous effect may now beobtained also for non-symmetrical positions of the resilient means.

It is noted that a certain deviation of the direction of the force fromperpendicular to the plane of the PCB is allowable. Thus, the springconstants may vary from each other by a predetermined amount orpercentage, usually caused by manufacturing imperfections.

As mentioned above, the distances to the centre of the component maydeviate by a predetermined amount or percentage, as long as thedirection of the force remains within tolerable angles of theperpendicular direction.

Thus, usually, it would be acceptable that the spring constants varywith up to 10% of a mean value of the constants of the resilientelements. Also, it would normally be acceptable that the distances ofthe individual biasing elements to the centre vary with up to 10% froman optimum or perfect position.

It is noted that an additional advantage is seen when the biasingelements engage the channel forming element and not e.g. the PCB. Whenengaging the PCB and deriving there from the force exerted by theresilient elements, the PCB will be affected thereby and flex. This maydestroy the PCB over time, also due to the vibrations and temperaturevariations normally seen in computers.

A second aspect of the invention relates to a method of operating theassembly of the first aspect, the method comprising:

-   -   providing power to the electrical components of the first PCB,    -   providing power to the electrical components of the second PCB,    -   operating the air forcing element to force air from the air        forcing element through the first end of the channel and toward        the second end of the channel and to draw air through the slit        and the space and into the channel.

In the following, preferred embodiments will be described with referenceto the drawing, wherein:

FIG. 1 illustrates a preferred embodiment from above,

FIG. 2 illustrates the embodiment of FIG. 1 from the side,

FIG. 3 illustrates a cross section of the embodiment of FIG. 1,

FIG. 4 illustrates a cross section of the embodiment of FIG. 1,

FIGS. 5 and 6 illustrate fixing means of the embodiment of FIG. 1, and

FIG. 7 illustrates positioning of biasing elements.

In FIG. 1, a data processing assembly 10 is illustrated from above. InFIG. 2, it is illustrated as a side view, in FIG. 3 as a cross sectionalong the A-line and in FIG. 4, a cross section along the B-line isillustrated. In FIGS. 5 and 6, details relating to the assembling of theassembly 10 are illustrated.

The assembly 10 comprises two printed circuit boards (PCB) 12 and 14,kept in position in relation to each other by an outer strengtheningelement 16, as well as a ventilator or fan 18. It is seen that the areadefined, in the plane of the PCBs 12/14, is taken up by the PCB 12 aloneor the PCB 14 along with the fan 18.

The PCBs comprise electronic components 20 on at least the sides thereoffacing each other, but components may also be provided on the sidesfacing away from each other.

The operation of the electrical components of the assembly 10 is thatthe components 20/20′ are powered and receive/generate/output data asdesired. Also, the components may comprise a power supply andinput/output means as indicated at 24. Also, the PCBs may each comprisea plug 22 which is adapted to interconnect the PCBs electrically inorder to interchange power/signals/information or the like.

The assembly may operate as a PCI card via externally accessibleterminals 12′. Also, the assembly may have a bracket 10′ as is requiredfor PCI cards.

The operation of the cooling of the present assembly is that the fan 18forces air into the assembly 10 and into a channel 30 defined by thePCBs 12/14 and the element 16 (see FIG. 4). This air will exit thechannel 30 at the other (lower in FIG. 1) end of the assembly 10, suchas through openings 16′ in the element 16.

The fan 18 preferably has (see FIG. 3) a lower surface 18′ between theactual fan and electrical components 20′ positioned there under in orderto increase the cooling thereof. Naturally, these components 20′ mayhave different heights, and the fan 18 may be forced, such as by aspring biasing, toward the highest of such components, and a thermallyconducting material, such as a paste, glue or foam, 28 may be providedbetween such lower components and the lower surface 18′.

In addition, the fan 18 has a number of parallel fins 18″, indicated inFIG. 1, through which the air entering the channel 30 passes and whichare thermally connected to the lower surface 18′ in order to increasethe cooling thereof.

The components which are cooled the best are the components 20′, whichusually will be the most power consuming, and thus heat producing,components. Naturally, the position of a component as a component 20′ atthe surface 18′, a component 20 within the channel 30 or a component 20positioned on the outer side of a PCB 12/14 will depend on the heatgeneration of this component during operation as well as the component'sability to withstand high temperatures.

Due to the flow of air through the channel 30 and due to a slit 16″provided in the element 16, air may also, due to the Venturi effect, bedrawn into the space in which the components 20′ are positioned and intothe channel 30. This provides an increased cooling of the elements 20′and also draws cold air, also cooled by the lower side of the element18′ facing the elements 20′, into the channel 30.

Assembly of the assembly 10 is performed in the following manner (see inparticular FIGS. 2, 5 and 6):

The strengthening element 16 is provided with a number of areas with acentral cut-out 32 and punched-out fins 34 which are used to fixelements 24 through which a channel 26 is provided. The elements 24 havea part fitting within the cut-out 32 so as to fix these in the directionacross the longitudinal direction of the element 16, and the fins 34thus will fix the element 24 to the element 16. The PCBs 12/14 then maybe fixed to each other and the elements 24 and thus strengtheningelement 16, using a bolt and nut through the channels 26.

The fan 18 is attached to the strength element 16 via a spring biasingin order to maintain a sufficient thermal connection to the elements 20′and the thermally conducting material 28. Thus, a plurality of parts 36of the element 16 are bent to be positioned over the fan 18, and a pin40 is provided in a hole 38 in each part 36 for guiding a spring 42 thenprovided between the part 36 and the fan 18 to force the fan 18 awayfrom the parts 36 and toward the elements 20′. Using the parts 36 of thestrengthening element 16 for biasing the fan 18 instead of a fasteningin relation to the PCB 12 saves space on the PCB 12. In addition, theforce may be applied to the component 20′ without having to derive theforce from the PCB 12, which would be the case, if the springs 42 wereconnected to the PCB and not the strengthening element 16.

Due to the biasing, it is preferred that the elements 36 are positionedsuch, in relation to a centre of the highest of the components 20′ thatthe force applied is balanced. This is illustrated in FIG. 7.

This may be obtained in multiple manners. Resilient elements 42 withdifferent spring constants may be used, depending on the positions ofthe parts 36 in relation to the centre of the highest component 20′, orthe positions of the parts 36 may be selected so that identical springs42 or at least elements with the same spring constants may be used.

Having the force and torque applied (force and distance to the centre ofthe highest component 20′) be directed directly downwardly at the centreof this component, the component 20′ is prevented from cracking, whichcould otherwise be the case, if the surface 18′ was to apply a force notperpendicular to the plane of the PCB 12.

In FIG. 7, the surface 18′ is illustrated as is the extent and positionof an element 20′ there under. The centre, c, of the surface 18′, andthat of the element 20′ is simple to determine.

The positions of two spring elements 42 are indicated at circles 1 and2, and two perpendicular directions are indicated by arrows a and b.From these positions, the optimal position of a third and any additionalelements 42 may be determined.

Due to it being desired for manufacturing purposes to have all resilientmeans 42 be identical (within manufacturing limits), the positions ofthe circles 1 and 2 and further resilient means 42 are determined simplyby the distances, projected on to the two directions, from the centre ofthe component 20′ to the positions 1,2 of the springs 42.

More particularly, the combined distances for all springs 42 positionedin one direction, along direction a, from the centre of the component20′ should be identical to or within a predetermined distance of thecombined distance for all springs 42 positioned in the oppositedirection, along direction a, from the centre of the component 20′.

The same should be true along the direction b, whereby a biasing isobtained using identical springs 42 which provides a force exerted bythe surface 18′ on the component 20′ directed perpendicularly to thesurface 18′ and thus on the upper surface of the component 20′.

1. An assembly comprising: a first PCB with a first side and a secondside, one or more first electrical components being positioned at thefirst side of the first PCB, a second PCB with a first side and a secondside, one or more second electrical components being positioned at thefirst side of the second PCB, the first side of the first PCB facing thefirst side of the second PCB, a channel forming element forming, with atleast part of the first sides of the first and second PCBs a channelhaving a first end and a second end, a slit being provided in thechannel forming element, and an air forcing element positioned to forceair through the channel from the first end thereof toward the second endthereof the air forcing element comprising a cooling surface and biasingelements biasing the cooling surface against at least one component ofthe first or second components, the cooling surface defining a spacewherein the at least one component is positioned, the slit beingpositioned so that air may be drawn there through, due to the venturieffect, into the space and into the channel.
 2. The assembly accordingto claim 1, further comprising one or more openings positioned at ornear the second end of the channel.
 3. The assembly according to claim1, wherein: the first PCB has a first outline, in a plane thereof, thesecond PCB has a second outline, in the plane, at least a part of thefirst and second outlines being overlapping, the channel forming elementblocking or closing any opening between the first and second PCBs at atleast part of a boundary of the overlapping part of the outlines.
 4. Theassembly according to claim 1, wherein the first PCB covers a firstarea, in a plane thereof, wherein the second PCB covers a second area inthe plane, the second area being positioned within the first area, andwherein the air forcing element covers a third area, in the plane, thethird area being positioned within a part of the first area not coveredby the second area.
 5. The assembly according to claim 4, wherein, inthe plane, the air forcing element is positioned closer to the first endof the channel than the second end of the channel.
 6. The assemblyaccording to claim 1, wherein the first and second PCBs are at leastsubstantially parallel.
 7. The assembly according to claim 1, whereinthe air forcing element comprises a number of fins through which the airentering the channel passes and which are thermally connected to thecooling surface.
 8. The assembly according to claim 1, wherein thebiasing elements comprise at least three resilient elements having atleast substantially the same spring constant, the resilient elementsbeing positioned so that the force exerted by the biasing elements andthe air forcing element on the at least one component is perpendicularto a plane on the PCB at which the at least one component is positioned.9. The assembly according to claim 8, wherein the biasing elements arepositioned so that, along each of two axes perpendicular to each otherand positioned in the plane, a first combined distance from a centre ofthe at least component to each biasing element positioned in onedirection along the axis in relation to the centre is within apredetermined distance from a second combined distance from the centreto each biasing element positioned in the opposite direction along theaxis in relation to the centre.
 10. The assembly according to claim 1,wherein the biasing elements abut the channel forming element.
 11. Amethod of operating the assembly of claim 1, the method comprising:providing power to the electrical components of the first PCB, providingpower to the electrical components of the second PCB, operating the airforcing element to force air from the air forcing element through thefirst end of the channel and toward the second end of the channel and todraw air through the slit and the space and into the channel.